Public Broadcasters Want Digital Interference Examined

The Corporation for Public Broadcasting seeks proposals to conduct a study of digital radio interference – both existing and projected – in 75 radio markets around the country, including the top 50. According to the RFP announcement, “CPB is concerned with the disenfranchisement of listeners due to the loss of services public radio currently provides to them and the underperformance or lack of HD service…when the conversion of public radio stations to HD is complete.”

The document itself notes, “CPB has received reports that existing analog listeners have lost reception of their favorite public radio station when new HD signals have gone on the air.”

This is one of HD Radio’s dirty little secrets. In order to accommodate the simultaneous broadcast of both an analog and digital signal, all radio stations will effectively double their spectral footprints (AM stations triple their bandwidth when they broadcast in hybrid mode). Fattening the signals of every radio station is bound to cause interference between stations located near each other on the dial.

Indeed, this problem was prevalent in the technical studies HD Radio’s developer, iBiquity Digital, and the National Radio Systems Committee submitted to the FCC for certification of the technology. Members of the public reported hearing the interference themselves. However, the increased potential for interference was dismissed by HD Radio’s cheerleaders as the price of going digital, and well worth it.

Now, as more radio stations put HD signals on the air, the potential for interference between them all increases. iBiquity’s technical studies were by no means comprehensive on this issue, by which I mean they did not investigate the interference problem much beyond acknowledging it, running some lab simulations, and checking to see if their test stations, the lone HD signals in their markets at the time, raised any new noise. The CPB proposal expects that the interference problem will get worse as more stations go digital.

Most alarmingly, this is already resulting in a loss of existing analog service to real people – a decrease in diversity on their local radio dial. iBiquity estimated there would be less than a 1% chance of this happening. Maybe it got carried away with decimal placement.

It’s too late to put this genie back in the bottle. Listeners who lose their favorite stations due to digital interference can either fork out the three-digit sum for an HD radio receiver (which won’t bring back reception of the station they want, but at least they’ll be able to enjoy the bells and whistles of those they can still get) – or they can suck it.

The FCC’s not likely to intervene: it’s already endorsed the HD Radio framework as the “de facto standard” for digital audio broadcasting in the United States, and requires only informal notice from stations who desire to throw up hybrid signals. In fact, the FCC never independently tested the in-band, on-channel (IBOC) framework that HD Radio is built upon, and never expressed any willingness to.

The FCC also set HD Radio’s bar for adoption criminally low, decreeing that it only had to be “superior to analog” in order to receive the rubber-stamp. That obviated the need for a comparative analysis between the many different DAB protocols that exist in the world. The broadcast industry got a proprietary DAB system it makes money from just by using; the listener, that “public” in “the public interest,” gets “buzz saw” noises on FM and “frying bacon effect” hash on AM.

To its credit, National Public Radio has long been a skeptic of HD Radio technology, and developed the multicasting functionality which is now being used as HD Radio’s major selling point. It will be interesting to see what the CPB-sponsored study discovers. But it’ll be awhile: applications from interested contractors are due on May 23, and once CPB awards the project it expects the study to take at least a year to complete.